1. Field of the Invention
The present invention relates to acoustic transmitting antennas which are in the shape of a ring and which can be dismantled. Such antennas are particularly useful for long range low frequency sonars.
2. Discussion of the Background
From the patent application Ser. No. 09/415,587 lodged by the company THOMSON-CSF on Dec. 23, 1994 under the title xe2x80x9cPre-stressed ring-shaped acoustic transducerxe2x80x9d and published on Jun. 4, 1996 under U.S. Pat. No. 2,728,755 there is known a transducer of this type essentially characterized in that the transmitting piezoelectric ring is produced in the form of segments placed inside a metal or composite annulus forming a hoop. These segments are separated from each other by metal parts in the shape of wedges. A screw-based device makes it possible to move the wedges towards the centre of the ring, which tends to separate the segments from one another. The segments are thus pressed against the hooping annulus and a pre-stressing of all the segments is obtained. A major advantage of this construction is that the device is thereby made such that it can be entirely and very easily dismantled, in order to be able, for example, to replace a defective part. Furthermore, it is very easily possible to adjust the pre-stressing by adjusting the screws until the desired characteristics, which are then continuously measured during this action, are obtained.
Such a transmitting transducer can easily be made with a diameter situated within a relatively wide range of dimensions. It is however more difficult, for both mechanical and acoustic reasons, to manufacture a transducer of this type with a relatively large height.
In order to obtain a sufficient transmitting power, which is known to be necessary in the low frequency ranges to which this type of transducer applies more particularly, it is therefore necessary to use several separate transducers of the same type. This can be done, for example, by fixing the transducers on a common frame which holds them at a suitable distance in order to obtain the desired acoustic characteristics. The presence of such a frame of course gives rise to an increase in the inactive mass with respect to the active mass constituted by the transducer elements themselves.
In certain cases, for a hull sonar for example, this does not present very big disadvantages. On the contrary, in other cases, in particular when the transmitting antenna is placed in a body towed by a boat, it is necessary to have the lowest possible weight in order to consequently reduce the mass of the towing cable both to reduce the drag and to facilitate the handling of this cable.
In order to be able to reduce this inactive mass, the invention proposes an annular acoustic transmitting antenna which can be dismantled, of the type comprising at least one pre-stressed ring formed from a set of piezoelectric segments grouped in order to form substantially identical sectors, end pieces fixed to these sectors in order to delimit wedge-shaped gaps between them, and wedge-shaped tightening keys adapted to these gaps and placed in them, a shaping hoop allowing all the sectors to be held, and means for allowing the tightening keys to slide towards the inside of the ring for pre-stressing the segments against the hoop, characterized in that it comprises a set of substantially identical rings superimposed upon each other in such a way that the tightening keys are facing each other, two profiled annuli of the same diameter as that of the pre-stressed rings and placed respectively at the two ends of the stack, and a set of fixing tie-rods traversing respectively the groups of superimposed keys by the intermediary of longitudinal holes bored in these keys in order to be fixed to the profiled annuli in order to press the rings against each other.
According to another characteristic, it comprises two jackets made of elastic material respectively covering the outside and inside faces of the cylinder formed by the stack of rings, and each comprising rims which anchor in peripheral grooves formed in the faces of the profiled annuli located on the other side from the faces of these annuli which bear on the rings.
According to another characteristic it furthermore comprises two ring-shaped flanges respectively fixed on the said surfaces of the profiled annuli in order to maintain the said rims in the said peripheral grooves.
According to another characteristic, it comprises insulating rings inserted between the superimposed rings.
According to another characteristic, it furthermore comprises rings made of an elastic material interposed between the profiled annuli and the insulating rings located under these annuli in order to decouple the rings acoustically from the structure supporting them.
According to another characteristic, the fixing tie-rods form screws whose heads bear on the outside face of one of the profiled annuli and whose other ends are threaded and screw into blind tapped holes, bored on the inside face of the other profiled annulus.
According to another characteristic, the feed connector of the antenna and the latter""s inflation nozzle are fixed on elastic supports which are themselves fixed on the outside surface of the inside protective jacket of the antenna.